Video generator

ABSTRACT

A video generator having means for selectively reading out one of many patterns recorded on a first track of a magnetic disc and repeatedly writing this pattern on a second track. The pattern at a desired position on the second track is solely read out to be written on a third track of the magnetic disc, and the video signal thus recorded on the third track is displayed on a CRT display.

United States Patent [151 3,699,565 Nagai [4 Oct. 17, 1972 [54] VIDEO GENERATOR 3,165,045 1/1965 Troll ..340/324 A X 72 Inventor; Hiroshi Nagai Chigasaki, Japan 3,205,344 9/1965 Taylor et al ..340/324 A X 3,298,013 1/1967 Koster ..340/324 A [731 Asslgmfi Him", Japan 3,396,377 8/1968 Strout ..340/324 A [22] Filed: May 3, 1971 Primary Examiner-David L. Trafton [21] Appl' 139506 Attorney-Craig, Antonelli & Hill [30] Foreign Application Priority Data [5 7] ABSTRACT y 4, 1970 Japan --45/37518 A video generator having means for selectively reading out one of many patterns recorded on a first track [52] "340/324 340/1741 340/1741 P of a magnetic disc and repeatedly writing this pattern [5 l Int. Cl ..G06f 3/14 on a second track The pattern at a desired position on [58] Fleld Search "340/324 I741 174'1 L the second track is solely read out to be written on a 56 R i d third track of the magnetic disc, and the video signal 1 e erences thus recorded on the third track is displayed on a CRT UNlTED STATES PATENTS p y- 2,832,064 4/1958 Lubkin ..340/l74.1 P 3 Claims, 5 Drawing Figures VIDEO Am 59 2 6 7 /6 t l we 43 e 5? /7 2/ la 27 %;5 W050 L HO/P sr/vc 3 {W 3 PULSE GEL/ll f2 23 4 VIDEO PULSE .4 55mm fi C/(T 6K7 \22 T l 1 J M 37i4a l56 CHARACTER Ll/VE 38 30 H0)? P05 L an? PATENTEBncr n 1972 sum 1 or 3 VIDEO 24 CHARACTER c005 NT 6K7 v x m 5 2 A \7 4/ Y H. C TMM M l e A v5 6 w 3 wm lJ W5 7 SSNK WK WP 1k K R5 m 3% 2. m w mum AR Rm .7 E 19. HW 0 6 0 x 6 5 INVENTOR MRos'm Nam VIDEO GENERATOR BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to a video generator.

2. Description of the Prior Art Teletype apparatus connected to computers have generally been employed heretofore as a means for carrying out man-machine communication. However, to meet the recent demand for handling information at a higher speed with better efficiency, a display system of the kind displaying characters and any other patterns on a CRT (cathode-ray tube) on the basis of the video technique used in television is gradually replacing the conventional teletype apparatus adapted for printing characters on a sheet of paper. The CRT display is advantageous over the conventional apparatus in that not only man-machine communication of data can be carried out at high speeds but also data displayed on the viewer screen can be visually checked so that necessary correction and re-touch can be easily made on the displayed data. The CRT display is further advantageous in that printed data need not be kept at hand due to the fact that necessary information can be immediately obtained at any time when so required and thus storage of information media, for example, preservation of printed matters becomes unnecessary. In a system including such a CRT display for displaying character information, a character generator which converts digital information forwarded to or transmitted from the system into video information to be displayed on the CRT occupies a considerable proportion of the whole system. Further, due to the function of the CRT which displays a televised moving picture, the scene is renewed at a rate of more than 30 times per second. According to this system, digital information stored at the receiving or transmitting end is read out one character after another and is then converted into video information. Thus, associated control means are required to continuously operate for the renewal of the scene. The above fact means that a set of a character generator and associated control means is required for each CRT, and this is a great hindrance to the desired reduction in the cost of the CRT display system.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a video generator including a character generator and associated control means capable of simultaneously serving a plurality of CRT displays.

Another object of the present invention is to provide a video generator whose cost per display is quite low.

The video generator according to the present invention is provided with a magnetic disc which has a number of concentric tracks. These tracksinclude a clock track on which clock pulses are recorded at equal intervals, a plurality of pattern tracks on which various kinds of characters are recorded at an interval equal to the interval between the clock pulses recorded on the clock track, a transfer track and at least one display track. One complete rotation of the magnetic disc corresponds to one scene displayed on the CRT display, and they are in synchronism with each other. The CRT display displays successively the characters written on the display track. All the characters to be displayed are recorded on the pattern tracks, and in response to the application of a character code from external means, the corresponding character is read out from the pattern tracks to be repeatedly written on the transfer track at an interval equal to the interval between the clock pulses recorded on the clock track. Therefore, the transfer track is entirely filled with a train of the selected single characters which are written on such track at an interval equal to the interval between the clock pulses. In response to a display position signal, the character at the corresponding position on the transfer track is written on the display track at the same position with respect to the clock. Display means reads out successively the characters written on the display track and displays such characters on the CRT display so that the desired characters can be displayed at the desired positions on the CRT display The present invention which utilizes a magnetic disc is advantageous in that associated control means are free from continuous operation for the scene renewal at a rate of more than thirty times per second.

A plurality of display tracks may be provided and connected to respective CRT displays so that these CRT displays can be simultaneously controlled and the cost of the system per CRT display can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing the detailed structure of the video switching circuit and associated elements shown in FIG. 1.

FIG. 3 is a diagram showing the detailed structure of the control circuit shown in FIG. 1.

FIG. 4 is a diagrammatic view illustrating the manner of transferring a character from a pattern track to a transfer track.

FIG. 5 is a diagrammatic view illustrating the manner of repeatedly recording the character on the transfer track and transferring the character from the transfer track to a display track.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is shown a video generator embodying the present invention which includes a magnetic disc 3 adapted to be continuously driven in a direction of the arrow 5 by a servomotor 4. A number of concentric tracks are provided on the magnetic disc 3, and a number of magnetic beads are associated with the respective tracks. The outermost track is a clock track 7 on which clock pulses are recorded at equal intervals to be read out by as associated magnetic head 6. The clock pulses read out by the magnetic head 6 are applied to a pulse circuit 12 in which they are subject to wave shaping and amplification and are then applied to a character horizontal position counter 13 which counts the horizontal position of characters. When the character horizontal position counter 13 counts a fixed value, an overflow output appears from the horizontal position counter 13 to be applied to a line counter 15 by a lead 14. The character horizontal position counter 13 is reset to its initial value or 0 after having applied its overflow output to the line counter 15. This overflow output is also applied to a servo circuit 22 to which the output from a horizontal synchronizing pulse generator 21 is applied by a lead 23. The servo circuit 22 compares the overflow output applied from the character horizontal position counter 13 with the horizontal synchronizing pulses applied from the horizontal synchronizing pulse generator 21 so as to ensure regular rotation of the magnetic disc 3. The horizontal synchronizing pulses are also applied to a CRT display 1 to act as a signal for starting the horizontal scanning in the CRT display 1. 1n the CRT display 1, a viewer screen 2 is scanned according to the scanning method employed in television and horizontal scanning rasters v appear in synchronism with the horizontal synchronizing pulses. Thus, the scanning in the CRT display 1 and the rotation of the magnetic disc 3 are in synchronism with the horizontal synchronizing pulses generated by the horizontal synchronizing pulse generator 21.

An index pulse track 16 is disposed adjacent to the clock track 7. A single pulse or index pulse is recorded on the circumference of the index pulse track 16 and this pulse is read out by an associated magnetic head 17. The index pulse read out by the magnetic head 17 is applied by a lead 18 to a pulse circuit 19 which is similar to the pulse circuit 12. The output from the pulse circuit 19 is applied by a lead 20 to the character horizontal position counter 13 and line counter to reset same.

The magnetic disc 3 is further provided with a plurality of pattern tracks 8. Character patterns of all the characters including the letters of the alphabet, Arabic numerals and special symbols used for display are recorded in the form of an analog video signal on the pattern tracks 8 at an interval equal to the interval between the clock pulses recorded on the clock track 7. The character patterns recorded on the pattern tracks 8 are read out by associated video heads 27 to be supplied to a video read-out amplifier 40.

FIG. 4 shows one of the pattern tracks 8 and the characters are shown in the same form as when they are displayed on the CRT display 1 for the convenience of easy understanding. FIG. 4 also shows the clock pulses 11 recorded on the clock track 7 and it will be seen from FIG. 4 that the characters are recorded on the pattern track 8 at an interval equal to the interval t between the clock pulses 11.

A transfer track 43 is disposed adjacent to the outermost pattern track 8. A magnetic head 44 is connected to the video readout amplifier 40 and to a video writein amplifier 42, and a magnetic head 47 is connected to the video write-in amplifier 42. The transfer track 43 is associated with these magnetic heads 44 and 47, and a character pattern selected from one of the pattern tracks 8 is transferred to the transfer track 43 from such pattern track 8. The magnetic beads 44 and 47 are spaced apart by one character, that is, by the pulse interval of the clock pulses recorded on the clock track 7, and for the reason which will be described later, a train of single character patterns are written on the entire circumference of the transfer track 43.

The magnetic disc 3 is further provided with a display track 58. The display track 58 is associated with a magnetic head 57 connected to the video write-in amplifier 42, and the character pattern transferred to the transfer track 43 is written by the head 57 on the display track 58. The display track 58 is further associated with another magnetic head 59. This magnetic head 59 is connected to the CRT display 1 through a video amplifier 60 so that the character pattern on the display track 58 can be displayed on the viewer screen 2 of the CRT display 1. One complete rotation of the magnetic disc 3 corresponds to one scene displayed on the viewer screen 2, and therefore, the display track 58 has a number of positions which correspond to the respective displaying positions on the viewer screen 2. For instance, the starting point of the display track 58 corresponds to the first character in the first line on the viewer screen 2.

In the CRT display 1, 30 rasters constitute one line and thus one character is constituted by 30 rasters. The CRT display 1 displays l0 lines each consisting of 20 characters and the fly-back time of each raster is selected to be equal to the period of two characters, that is, 2t in which t is the clock pulse interval. 6,600 clock pulses are recorded on the clock track 7 at equal intervals. The character horizontal position counter 13 counts 22 clock pulses and is resetafter applying its overflow output to the line counter 15 in response to the 23rd clock pulse. The count of the line counter 15 is advanced by l after having been applied with 30 overflow pulses from the character horizontal position counter 13. Thus, the character horizontal position counter 13 and the line counter 15 indicate the angular position of rotation of the magnetic disc 3, and at the same time, indicate the displaying position on the CRT display 1.

A character code for the purpose of display of a specific character is applied to a decoder 25a (FIG. 3)

I in a control circuit 25 by a lead 24. The index pulse is applied from the pulse circuit 19 to the control circuit 25 by the lead 20 so that the control circuit 25 operates in synchronism with the index pulse. The decoder 25a decodes the character code applied thereto and delivers a track selecting level signal 26, a character horizontal position specifying signal 28, a line specifying signal 29 and a position selecting level signal 30. The track selecting level signal 26, character horizontal position specifying signal 28 and line specifying signal 29 represent the position of the character of the applied character code on the pattern track 8. Suppose that a character code representing the character A is applied by the lead 24. It is known from FIG. 4 that the position of the character A on the magnetic disc 3 corresponds to the fourth position in the first line. Therefore, the character horizontal position specifying signal 28 and the line specifying signal 29 delivered from the decoder 25a are 00100 and 0000 respectively according to the binary notation. Further, another output from the decoder 25a acts to set a holding circuit 25b to be utilized as a signal which will be described later The character horizontal position specifying signal 28 is applied to a gate 31, while the line specifying signal 29 is applied to a gate 32. Simultaneously with the application of the character horizontal position specifying signal 28 and the line specifying signal 29 to the respective gates 31 and 32, the position selecting level signal 30 is applied to these gates 31 and 32 from the decoder 25a for opening these gates. As a result, these specifying signals 28 and 29 are applied through the gates 31 and 32 to comparators 33 and 34 respectively. The comparator 33 compares the output 35 from the character horizontal position counter 13 with the output from the gate 31, and when these two signals coincide with each other, a coincidence output appears from the comparator 33 on a lead 37. The comparator 34 compares the output 36 from the line counter with the output from the gate 32, and when these two signals coincide with each other, a coincidence output 1 appears from the comparator 34 on a lead 38. The appearance of the coincidence signals from both these comparators 33 and 34 shows the fact that the desired character pattern A is located beneath the associated video head 27 The coincidence outputs from the respective comparators 33 and 34 and the position selecting level signal 30 from the decoder 250 are applied to a gate 390 in a video switching circuit 39 as shown in FIG. 2. The gate 39a is opened solely when the coincidence signals appears on both the leads 37 and 38. Since there are a plurality of pattern tracks 8, the specific track 8 having the character pattern A thereon must be specified. To this end, the track selecting level signal 26 obtained by decoding the given character code is applied from the decoder 25a to gates and amplifiers 40a, 40b and 400 in the video read-out amplifier 40 so as to select only one video head 27. Therefore, the selected video head 27 associated with the specific pattern track 8 is connected to the head 44 associated with the transfer track 43 through the gate 40a, 40b or 400, video signal lead 41, gate 39a and amplifier 42b so that the character pattern A on the specific pattern track 8 is written on the transfer track 43 by the head 44. Further rotation of the magnetic disc 3 advances the count of the character horizontal position counter 13. As a result, the coincidence output having appeared on the lead 37 disappears to close the gate 39a and no information is written on the transfer track 43 by the video head 44. Upon counting 23 clock pulses 11, the character horizontal position counter 13 delivers an overflow pulse and is reset to the initial state of 00000. However, due to the fact that the line counter 15 is designed so that 30 overflow pulses applied from the character horizontal position counter 13 advances the count by l, the coincidence output is continuously delivered from the comparator 34 to appear on the lead 38 during this period of time, The coincidence output is delivered from the comparator 33 to appear on the lead 37 again when further rotation of the magnetic disc 3 advances the count of the character horizontal position counter 13 to 00011 again. Thus, the gate 390 is opened in response to the application of both the coincidence outputs from the comparators 33 and 34 by the leads 37 and 28, and 38, video head 44 associated with the transfer track 43 is connected to the selected video head 27 associated with the specific pattern track 8 to write the character pattern on the transfer track 43. Since one character is constituted by 30 rasters, on-off of the coincidence output on the lead 37 is repeated 30 times at an interval of 23 clock pulses during the period of time in which the coincidence output appears continuously on the lead 38, that is, during the period of time of 660 clocks, and the gate 39a is opened 30 times during one complete rotation of the magnetic disc 3. In other words, the pattern track 8 is in the form of a series connection of 130 rasters or scanning lines 10 (30 rasters per character X 10 lines), or more precisely, referring to FIG. 4, the pattern track 8 comprises a raster train in which the rasters 10 are successively connected in series from above from a direction shown by the arrow 9 toward a direction shown by the arrow 45. Therefore, a character pattern on the pattern track 8 comprises a series of rasters l0 ranging from the first 30th raster 10 with the adjacent rasters being spaced apart by 23 clock pulses. Thus, the gate 39a is opened 30 times at an interval of 23 clocks during one complete rotation of the magnetic disc 3.

Even when the character pattern A is transferred from the pattern track 8 to the transfer track 43, the character pattern is merely transferred to a different track to occupy the same position with respect to the specific clock and cannot be displayed at the desired position on the viewer screen 2. If the character pattern A on the transfer track 43 is displayed on the viewer screen 2, it will be displayed at the fourth character position in the first line. This character pattern A can be displayed at any desired position on the viewer screen 2 by writing the character pattern A on all the positions of the transfer track 43 so that the same character A may be displayed over the entire surface of the viewer screen 2. By this arrangement, the character A can be displayed at any desired position on the viewer screen 2 by selectively deriving the video signal representative of the character A from this position of the track for displaying the character A.

The transfer of the character pattern A from the pattern track 8 to the transfer track 43 is completed upon one rotation of the magnetic disc 3. After this transfer operation, the indexpulse is applied to an AND gate 25c by the lead 20 to open the AND gate 250 thereby setting a holding circuit 25d and resetting the holding circuit 25b. Theoutput from the holding circuit 25b is applied by a lead 48 to agate 39c in the video switching circuit 39 to open the gate 390. As a result, the head 44 is connected through an amplifier 40d, gate 390 and amplifier 42a to the head 47 which is spaced apart from the head 44 by one clock position on the same transfer track 43. Thus, the character pattern A having been read out by the head 44 is written by the head 47 at a position which is advanced by one clock position. After the period of time corresponding to one clock pulse interval, the video signal having been written by the hand 47 is read out by the head 44 and this video signal is written by the head 47 again at a position which is advanced by one clock position. The above operation is repeated during the rotation of themagnetic disc 3 so that the character A is repeatedly written on the transfer track 43. The position at which the video signal is transferred from the patterntrack 8 to the transfer track 43 varies depending on the character pattern, and therefore, the repeated writing described above does not necessarily take place in response to the appearance of an index pulse due to the decoding of a character code. In the case of the character A, the repeated writing takesplace in a period of time corresponding to 4 clocks after an index pulse has appeared. The character A is not yet written on the entire circumference of the transfer track 43 at the time at which the next index pulse appears, and the magnetic disc 3 must be rotated for a period of time corresponding to 4 clocks in order that the character A can be written on the entire circumference of the transfer track 43. In other words, the magnetic disc 3 must make two complete rotations in order that the same character can be written on the entire circumference of the transfer track 43. To this end, the lead 48 is also connected to a holding circuit 25f so as to maintain the signal until the magnetic disc 3 completes two rotations thereby to keep open the gate 39c during this period of time. Thus, the character A is written on the entire circumference of the transfer track 43. When the pattern on the transfer track 43 is displayed on the viewer screen 2, the character A will be displayed over the entire surface of the viewer screen 2 as seen in FIG. 5. The character A will also be written on the portions corresponding to the fly-back period of the two character length, but this character is not displayed.

The character pattern A repeatedly written on the transfer track 43 is then transferred to the display track 58. The operation for transferring this character pattern A to the display track 58 so as to display the character A at a desired position on the viewer screen 2 will now be described. At the time at which the repeated writing of the character pattern A on the transfer track 43 is completed, the holding circuit 25f is in its set position, and in response to an index pulse appearing thereafter, an AND gate 253 is opened to set a holding circuit 25h in place of the holding circuit 25f. The AND gate 25g delivers a specified position advancing pulse which is applied to a horizontal position specifying counter 50 by a lead 49. The count of the horizontal position specifying counter 50 is advanced each time the advancing pulse is applied thereto. The horizontal position specifying counter 50 is reset to after counting 20 which is equal to the number of characters to be displayed in one line on the viewer screen 2, and at the same time, the count of a vertical position specifying counter 51 is advanced. The count of these two counters 50 and 51 is advanced in the manner above described in response to the application of a character code to the control circuit 25 thereby to indicate the position of the specific character on the viewer screen 2. The output lead 56 of the holding circuit 25h is connected to gates 54 and 55 so that the signal applied from the holding circuit 25h opens these gates 54 and 55 with the result that the outputs 52 and 53 from these two counters 50 and 51 are applied to the comparators 33 and 34 respectively. As described previously, the respective outputs 35 and 36 from the character horizontal position counter 13 and line counter represent the angular position of rotation of the magnetic disc 3 corresponding to the scanning position for the viewer screen 2, and these two outputs 35 and 36 are applied to the respective comparators 33 and 34 as another input thereto. The coincidence outputs appearing on the output leads 37 and 38 of the respective comparators 33 and 34 and the signal appearing on the output lead 56 of the holding circuit 25h are applied to a gate 39b to open same thereby connecting the head 57 associated with the display track 58 to the head 44 associated with the transfer track 43 so that the character pattern A at the position coinciding with the displayed position on the viewer screen 2 is written by the head 57 on the display track 58 at the same position with respect to the specific clock. The head 59 associated with the display track 58 is connected to the CRT display 1 so that the pattern on the display track 58 is displayed on the viewer screen 2 of the CRT display 1. Since the rotation of the magnetic disc 3 is in synchronism with the scanning on the viewer screen 2, the position on the display track 58 is exactly displayed as the position on the viewer screen 2. For example, when the horizontal position specifying counter 50 and the vertical position specifying counter 51 indicate that the character A be displayed at the first character position in the first line on the viewer screen 2, the first character pattern A on the transfer track 43 corresponding to this position is selected and written at the first clock position of the display track 58. In writing the video signal on the display track 58, the index pulses or vertical synchronizing signal appearing on the lead 20 and the overflow pulses appearing on the lead 14 are superposed on the video signal so as to obtain a so-called composite video signal and this composite video signal is written on the display track 58.

The above description has referred to the case in which the character pattern A is selected and written at a desired position in response to the application of the character code representative of the character A by the lead 24. It will be seen that a video signal representative of a desired character is read out from the pattern track 8 and is repeatedly written on the transfer track 43 so that the character can be displayed at any desired position on the viewer screen 2. The character pattern at the desired position is read out from the transfer track 43 having a series of such character patterns repeatedly written thereon and is written on the display track 58. In this manner, various characters are successively written on the display track 58, and the video head 59 associated with the display track 58 reads out these character patterns in response to the synchronizing signal so as to display the characters on the viewer screen 2 of the CRT display 1.

According to the present invention, a plurality of display tracks 58 may be provided and connected to a plurality of CRT displays 1 respectively so as to sim ultaneously control these CRT displays 1. In this case, gates and amplifiers similar to the gates and amplifiers 40a-40 disposed in the video read-out amplifier 40 may be provided in the video write-in amplifier 42. An external signal indicating a specific display number may be applied to the control circuit 25 to open the gate and amplifier for the display track corresponding to the specific display number so that a specific character pattern is transferred from the transfer track to be written on the specific display track. Once the character pattern is selected and written on the display track, the operation for generating the character pattern is unnecessary because the character pattern to be displayed exists on the display track already. Thus, the system is now free to operate for the selection and display of characters for other viewer screens and can singly serve the character selecting operation for all the CRT displays.

I claim:

1. A video generator comprising a continuously driven magnetic disc provided with a clock track having clock pulses recorded thereon at equal intervals, a pattern track having various kinds of character patterns recorded thereon at an interval equal to the interval between the clock pulses recorded on said clock track, a transfer track and a display track, display means operating in synchronism with said magnetic disc to read out the character patterns on said display track for successively displaying the characters on a display unit, means for reading out a specific character pattern from said pattern tracks in response to the application of a specific character code to repeatedly write said character pattern on said transfer track at an interval equal to the interval between the clock pulses recorded on said clock track, and means responsive to a display position signal for writing the character pattern occupying the specified position of said transfer track on said display track at the same position with respect to the specific clock.

2. A video generator as claimed in claim 1, in which said magnetic disc is provided with a plurality of display tracks, and a plurality of display units are connected to said display tracks respectively so that said display units can be simultaneously controlled.

3. A video generator as claimed in claim 1, in which said transfer track is associated with two magnetic heads which are spaced apart by one clock pulse interval of the clock pulses recorded on said clock track, and the head disposed on the trailing side with respect to the directionof rotation of said magnetic disc reads out the character pattern from said transfer track, while the other magnetic head disposed on the leading side writes the character pattern on said transfer track so as to repeatedly write the character pattern on said transfer track. 

1. A video generator comprising a continuously driven magnetic disc provided with a clock track having clock pulses recorded thereon at equal intervals, a pattern track having various kinds of character patterns recorded thereon at an interval equal to the interval between the clock pulses recorded on said clock track, a transfer track and a display track, display means operating in synchronism with said magnetic disc to read out the character patterns on said display track for successively displaying the characters on a display unit, means for reading out a specific character pattern from said pattern tracks in response to the application of a specific character code to repeatedly write said character pattern on said transfer track at an interval equal to the interval between the clock pulses recorded on said clock track, and means responsive to a display position signal for writing the character pattern occupying the specified position of said transfer track on said display track at the same position with respect to the specific clock.
 2. A video generator as claimed in claim 1, in which said magnetic disc is provided with a plurality of display tracks, and a plurality of display units are connected to said display tracks respectively so that said display units can be simultaneously controlled.
 3. A video generator as claimed in claim 1, in which said transfer track is associated with two magnetic heads which are spaced apart by one clock pulse interval of the clock pulses recorded on said clock track, and the head disposed on the trailing side with respect to the direction of rotation of said magnetic disc reads out the character pattern from said transfer track, while the other magnetic head disposed on the leading side writes the character pattern on said transfer track so as to repeatedly write the character pattern on said transfer track. 